The wreck of the Titanic was discovered during a search for what?

In 1985 the oceanographer and explorer Robert Ballard was aboard the French research ship Le Suroît, using side-scan sonar to search for the wreck of the Titanic. When Le Suroît was recalled, Ballard transferred to a ship from Woods Hole, the R/V Knorr. This trip was financed by the U.S. Navy for secret reconnaissance of the wreckage of two nuclear-powered attack submarines, USS Scorpion and USS Thresher, which sank in the 1960s, and not for Titanic.

In 1982 Ballard had approached the Navy about his new deep-sea underwater robot craft, the Argo and his search for Titanic. The Navy wanted to find out what had happened to the submarines and concluded that Argo was their best chance. They agreed to finance Ballard's Titanic search if he first searched for the submarines, found out the state of their reactors and discovered whether their radioactivity was affecting the environment. Ballard was placed on temporary active duty in the Navy, in charge of finding and investigating the wrecks.